Exacerbations of allergic bronchopulmonary aspergillosis (ABPA) are characterized by chest roentgenographic infiltrates, peripheral blood eosinophilia, and elevation of total serum IgE. Also elevated are serum immunoglobulin antibodies directed against Aspergillus fumigatus, IgE-Af, serum IgG-Af, and serum IgA-Af. We measured serum IgA-Af, IgA1-Af, and IgA2-Af by ELISA to determine whether elevations of IgA-Af occurred before or during an exacerbation (like IgG-Af) or after (like IgE-Af). Ten exacerbations of ABPA were studied in seven patients with an average of 10 serial sera per patient analyzed. We used an indirect amplified ELISA with Af initially sensitizing microtiter wells. A "serologic" rise of immunoglobulin Af was identified when optical densities were twice the baseline sera. Serum IgA-Af was elevated over baseline before (n = 5) and during (n = 1) the time of an exacerbation. Serum IgA1-Af was elevated over baseline before (n = 5) or at the time (n = 5) of an exacerbation in all 10 cases. Serum IgA2-Af was elevated before (n = 2) and during (n = 5) exacerbations. Analogous to total serum IgE and IgG-Af, these experiments demonstrate substantial elevations of serum IgA-Af, IgA2-Af, and particularly, IgA1-Af before or during exacerbations characterized by roentgenographic infiltrates. The data are consistent with a contributory role of IgA-Af in the pathogenesis of ABPA.